In the prior art it is known to use light for the storage of information in a thermoplastic film--see the D. S. Lo, et al, U.S. Pat. No. 3,995,280--or in a magnetic film--see the M. M. Hanson, et al, U.S. Pat. No. 4,040,039; for optically processing information--see the D. L. Fleming U.S. Pat. No. 4,087,809--or for optically correlating information--see the D. L. Fleming, et al, U.S. Pat. No. 4,123,142. In the E. J. Torok, et al, U.S. Pat. No. 3,752,563 there is taught the use of an optical system that includes a diffraction grating for the change of direction of an incident light beam. The diffraction grating includes a thin ferromagnetic film in which a plurality of parallel, straight stripe domains by their separation and orientation control the angle of deflection and the angle of rotation, respectively, of an incident light beam. Such diffraction grating has been used as a uni-directional device--see the G. F. Sauter, et al, patent application filed Dec. 27, 1977, Ser. No. 864,167, now U.S. Pat. No. 4,148,556--or a bi-directional device-- see the G. F. Sauter patent application filed Mar. 30, 1978, Ser. No. 891,881, now U.S. Pat. No. 4,168,107--for coupling a light beam to a dielectric waveguide, modulating the intensity of the coupled diffracted light beam and multiplexing the coupled diffracted light beam to any selected one of several optical fiber transmission lines.